Electric and hybrid vehicles have recently become a more common sight on roads worldwide. They have one thing in common and that is they all require a large and powerful rechargeable energy storage, for example a rechargeable battery. Such rechargeable batteries have a limited runtime every time it is recharged and a user typically has a way of monitoring an estimated currently available energy of the battery (e.g. in the form of estimated range reachable with the presently available energy).
The available power, or “state of power” (SoP), is a characteristic to monitor during operation of the vehicle. A battery management system of the vehicle typically continuously monitors (“online”) the currently available power. Furthermore, the battery management system may try to predict the future behavior of the battery during charging or discharging of the battery. Among the variables to monitor is the maximum charging and maximum discharging currents that can be applied without violating certain pre-known power limits of the battery.
A common approach for online monitoring of the state of power of a battery is to use an equivalent circuit model of the battery. The state of power is often estimated concurrently with the parameters of the equivalent circuit (e.g. resistances and capacitances), the state of charge (SoC), and the open circuit voltage (OCV), etc. The circuit parameters, SoC, and OCV depend on each other and SoP depends on the circuit parameters. However, since the time-scale of their dynamics, the reliability of a concurrent estimation may be questioned. Thus, the use of e.g. SoC or OCV for estimating the short term behavior of a battery relies on a relatively high degree on the accuracy of the estimates of SoC or OCV. For example, an error in the open circuit voltage because of poor modeling, or hysteresis or a bias in a current sensor may lead to errors in estimating the e.g. state of power of the battery.
An example of a method for determining battery predictive power limits is disclosed by U.S. Pat. No. 8,466,684. In U.S. Pat. No. 8,466,684, a maximum power limit may be predicted for a future time period based on the battery current and voltage in a time period preceding the future time period. However, the method disclosed by U.S. Pat. No. 8,466,684 suffers from poor adaptability to changes in demand of power, and in particular to rapid changes in demand of power from the battery.
Thus, there is a need for a more reliable and robust way of determining the state of power of a battery.